Further studies in flood tolerance of Betula papyrifera seedlings

Flooding of soil for 60 days drastically reduced height growth, cambial growth, dry weight increment, and relative growth rate of 150-day-old Betula papyrifera Marsh. seedlings. Comparisons of responses to flooding of 150-day-old and 230-day-old seedlings indicated important differences between the two age classes. Whereas the younger seedlings produced abundant adventitious roots on submerged portions of stems, the older seedlings did not. Flooding also induced much more leaf abscission in the older seedlings. Flooding generally reduced root-shoot ratios of both age classes, largely as a result of inhibition of growth and decay of root systems. However, root-shoot ratios were altered appreciably by formation of adventitious roots in the younger seedlings and by extensive leaf abscission in the older seedlings.     

Responses of ectomycorrhizal Populus tremuloides and Betula papyrifera seedlings to salinity

Roots of trembling aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.) seedlings were inoculated with Hebeloma crustuliniforme or Laccaria bicolor and treated with 25 mM NaCl for 6 weeks. Both tree species appeared to be relatively tolerant of the applied NaCl treatment and did not develop visible leaf symptoms that are characteristic of salt injury. Salt treatment reduced total dry weights in aspen and birch, but did not significantly affect transpiration rates and root hydraulic conductance. Salt-treated ectomycorrhizal aspen maintained higher root hydraulic conductance compared with non-mycorrhizal plants. Na and Cl concentrations increased in shoots and roots of mycorrhizal and non-mycorrhizal aspen and birch in response to NaCl treatment. Roots of NaCl-treated aspen inoculated with H. crustuliniforme had over twofold higher concentrations of Na compared with non-mycorrhizal NaCl-treated plants. Similarly to aspen, Na and Cl concentrations increased in roots and shoots of NaCl-treated birch seedlings. However, in birch, there were no significant differences in Na and Cl concentrations between mycorrhizal and non-mycorrhizal plants. The results suggest that salt exclusion by the ectomycorrhizal associations is host-specific or/and that the processes leading to salt exclusion are activated in ectomycorrhizal plants by a threshold salt level which may vary between plant species.     

不同地理种源西南桦苗木的耐热性研究

由于受全球气候变化的影响,近年来我国一些地区出现了异常高温天气,这越来越引起林业工作者的重视。以亚热带珍贵用材树种西南桦为研究对象,以采集于我国广西和云南两省区12个种源的西南桦种子所育苗木为实验材料,对不同种源苗木在41C高温处理下的生理指标(叶片电导率、净光合速率、蒸腾速率和根系活力)的变化进行了综合评价,来选择耐热性优良的种源。结果表明,各生理指标在高温处理后与处理前相比发生了较为明显的变化,其中,叶片电导率增高为对照温度(25C)的1．2倍,光合速率、蒸腾速率和根系活力则分别只有对照温度的60％、21％和6％;方差分析发现,在对照温度下,各生理指标在不同种源间的差别不明显,而在41C高温处理后,这种差异达到显著程度。用模糊数学的隶属度函数对参加试验的12个种源西南桦苗木的耐热性进行综合评价发现,凌云种源的耐热性最强,建议作为推荐优先发展的种源。     

The survival of some soil mites at different humidities and their reaction to humidity gradients

The survival at different humidities of 10 species of soil mites in larval, nymphal and adult stages has been investigated. The immature forms are almost as resistant as mature but differences exist between species. Moisture preferences were also investigated and some form of ortho-kinesis may explain the results.

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Zusammenfassung Acht Oribatiden- und zwei Uropodiden-Arten wurden einem Feuchtigkeitsgefälle von völliger Sättigung bis zu 13% rel. Luftfeuchtigkeit ausgesetzt. Erwachsene Pelops acromios, Cepheus dentatus und Odontocephus elongatus zeigten sowohl bei 10° wie bei 20° in allen Feuchtigkeitsstufen nach drei Tagen eine 100% ige Überlebensrate. Ceratoppia bipilis, Oribata gracilipes und Euzetes seminulum wiesen bei niederer Luftfeuchtigkeit erhöhte Sterblichkeit auf und bei 13% rel. Luftfeuchtigkeit betrugen ihre Überlebensraten nach drei Tagen 75, 55 bzw. 45%. Hermannia gibba, Platynothrus peltifer, Olodiscus integra und Cilliba cassidea zeigten unter 55% rel. Luftfeuchtigkeit alle einen plötzlichen Abfall der Überlebensrate und am Ende von drei Tagen blieben nur wenige Individuen am Leben. Die Fähigkeit der larvalen und Nymphenstadien, erniedrigte Luftfeuchtigkeit zu ertragen, war im allgemeinen etwas geringer als bei den Adulten, doch zeigten die Arten untereinander die gleiche relative Resistenz wie bei den Erwachsenen. In einer alternativen Wahlkammer, die ein Feuchtigkeitsgefälle aufwies, bevorzugten alle Arten die feuchtere Hälfte. Nur wenn die Wahl zwischen 94% und 100% rel. Luftfeuchtigkeit geboten wurde, bevorzugten P. acromios, C. dentatus und O. elongatus die geringere Feuchte. Die Ergebnisse weisen darauf hin, daß eine Form von Orthokinese vorliegt und noch kein Unterschied in der Anzahl der Individuen beobachtet wurde, die sich bei gleichmäßiger Feuchtigkeit von 10, 47 und 100% rel. Luftfeuchtigkeit bewegten. Im Vergleich zwischen feuchten und trockenen Bedingungen besteht kein wahr nehmbarer Sensibilitätsunterschied.

     

The role of cytoskeleton in stomata functioning

The main question in this review is of whether and how the cytoskeleton of guard cells is involved in stomata movements. The main function of stomata is the regulation of the rate of gas exchange between the plant environment and underlying plant tissues. As a result of special morphology and anatomy GCs form the stomatal pore. It can open or close in a controlled manner via internal or external signal-induced changes in GCs turgor pressure, volume and shape. The mechanism of stomata movement is a complex process. A network of actin microfilaments and microtubules, dynamic polymers collectively known as the cytoskeleton forms protein fibril systems in GCs. CT elements are dynamic structures, interconnected to different cell structures. The organization of CT during morphogenesis of stomata is very important in establishing the size and shape of GCs. It is well documented that AFs and MTs are involved in stomata movements and can modify the ability of GCs to respond to environmental and hormonal stimuli. Data gathered clearly suggest that the organization of CT elements is not a direct effect of stomata movements. Several investigation procedures for study of the CT role in stomata functioning, including GCs treatment with anti-CT drugs (disrupters or stabilizers), have been analyzed and discussed in this review but the question of what role AFs and MTs play in stomata movements and how they work still remains open. The availability of new CT visualization techniques and the usage of mutants to study this problem is a good perspective for further research.     

构树幼苗对接种丛枝菌根真菌的生长响应

利用石灰岩适生植物构树进行菌根真菌摩西球囊霉(GM)、地表球囊霉(GV)和透光球囊霉(GD)的单独接种(SI)、混合接种(CI)和不接种(N)处理试验,测定了构树幼苗生长3个月后的形态及生长指标.结果表明:接种VA真菌促进了宿主构树的生长,单株地上部分、地下部分生物量和全株生物量等生长指标均较对照组显著提高,4种处理下构树幼苗生物量较对照提高了2.49～8.19倍,其中CI处理生物量最大,而单株叶片数目与对照组没有显著差异.不同接种处理的构树幼苗生长响应不同.在SI处理中,GD对构树幼苗生长效应最大,而CI处理较SI处理对构树幼苗的促进效应更加明显.CI处理中地径、苗高和总叶面积分别是对照组的1.5、2.2和6.0倍.各处理中根冠比最大的为CI(0.446).说明宿主植物与菌种存在一定的选择性.     

The allometry of root production and loss in seedlings of Acer rubrum (Aceraceae) and Betula papyrifera (Betulaceae): implications for root dynamics in elevated CO2

Total root production (∑P), total root loss (∑L), net root production. (NP), and biomass production were determined for seedlings of Betula papyrifera and Acer rubrum in ambient and elevated CO₂ environments. ∑P, ∑L, and NP were calculated from sequential, independent observations of root length production through plexiglass windows. Elevated CO₂ increased ∑P, ∑L, and NP in seedlings of Betula papyrifera but not Acer rubrum. Root production and loss were qualitatively similar to whole-plant growth responses to elevated CO₂. Betula showed enhanced ∑P, ∑L, and biomass with elevated CO₂ but Acer did not. However, the observed effects of CO₂ on root production and loss did not alter the allometric relationship between root production and root loss for either Acer or Betula. Thus, in this experiment, elevated CO₂ did not affect the relationship between root production and root loss. The results of this study have important implications for the potential effects of elevated CO₂ on root dynamics. Elevated CO₂ may lead to increases in root production and in root loss (turnover) where the changes in root turnover are largely a function of the magnitude of root production increases.     

Gas-exchange analysis of chloroplastic fructose-1,6-bisphosphatase antisense potatoes at different air humidities and at elevated CO2

Gas-exchange measurements were performed to analyze the leaf conductances and assimilation rates of potato (Solanum tuberosum L. cv. Desireé) plants expressing an antisense construct against chloroplastic fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11) in response to increasing photon flux densities, different relative air humidities and elevated CO₂ concentrations. Assimilation rates (A) and transpiration rates (E) were observed during a stepwise increase of photon flux density. These experiments were carried out under atmospheric conditions and in air containing 500 μmol mol⁻¹ CO₂. In both gas atmospheres, two levels of relative air humidity (60–70% and 70–80%) were applied in different sets of measurements. Intercellular CO₂ concentration, leaf conductance, air-to-leaf vapour pressure deficit, and instantaneous water-use efficiency (A/E) were determined. As expected, assimilation rates of the FBPase antisense plants were significantly reduced as compared to the wild type. Saturation of assimilation rates in transgenic plants occurred at a photon flux density of 200 μmol m⁻² s⁻¹, whereas saturation in wild type plants was observed at 600 μmol m⁻² s⁻¹. Elevated ambient CO₂ levels did not effect assimilation rates of transgenic plants. At 70–80% relative humidity and atmospheric CO₂ concentration the FBPase antisense plants had significantly higher leaf conductances than wild-type plants while no difference emerged at 60–70%. These differences in leaf conductance vanished at elevated levels of ambient CO₂. Stomatal response to different relative air humidities was not affected by mesophyll photosynthetic activity. It is suggested that the regulation of stomatal opening upon changes in photon flux density is merely mediated by a signal transmitted from mesophyll cells, whereas the intercellular CO₂ concentration plays a minor role in this kind of stomatal response. The results are discussed with respect to stomatal control by environmental parameters and mesophyll photosynthesis. Received: 24 September 1998 / Accepted: 9 February 1999     

Production and utilization of extracellular slime by Pseudomonas solanacearum and its role on survival at different relative humidities

Pseudomonas solanacearum produced maximum slime with glucose and least with glycerol. With increasing concentration of glucose, slime production increased. The maximum slime production was observed in the medium containing 1% glucose. The slime contained sugars, sugar acids and amino acids. The bacterium utilized the slime as a sole source of carbon. The growth on slime was more or less comparable to the growth on 0.1% glucose. The viability of the bacterium in slime increased as the relative humidity (RH) decreased. At higher RH the slime absorbed moisture and the viability was reduced. The bacterium could survive only for short period at higher RH under sunlight not in shade. The sunlight seemed to accentuate the harmful effect of RH on the bacterium.     

The survival of Entomophthora spp. in mummified aphids at different temperatures and humidities

Entomophthora aphidis survived for at least 32 weeks at 0°C and 20 or 50% RH and E. thaxteriana for at least 16 weeks at 10°C and 20 or 50% RH in mummified infected pea aphids, Acyrthosiphon pisum. The fungi produced infective conidia when the aphids were moistened. This probably explains the survival of Entomophthora species infecting aphids during short periods when the weather is unsuitable for conidial discharge and host infection.     

Elevated CO2 interacts with herbivory to alter chlorophyll fluorescence and leaf temperature in Betula papyrifera and Populus tremuloides

Herbivory can influence ecosystem productivity, but recent evidence suggests that damage by herbivores modulates potential productivity specific to damage type. Because productivity is linked to photosynthesis at the leaf level, which in turn is influenced by atmospheric CO(2) concentrations, we investigated how different herbivore damage types alter component processes of photosynthesis under ambient and elevated atmospheric CO(2). We examined spatial patterns in chlorophyll fluorescence and the temperature of leaves damaged by leaf-chewing, gall-forming, and leaf-folding insects in aspen trees as well as by leaf-chewing insects in birch trees under ambient and elevated CO(2) at the aspen free-air CO(2) enrichment (FACE) site in Wisconsin. Both defoliation and gall damage suppressed the operating efficiency of photosystem II (ΦPSII) in remaining leaf tissue, and the distance that damage propagated into visibly undamaged tissue was marginally attenuated under elevated CO(2). Elevated CO(2) increased leaf temperatures, which reduced the cooling effect of gall formation and freshly chewed leaf tissue. These results provide mechanistic insight into how different damage types influence the remaining, visibly undamaged leaf tissue, and suggest that elevated CO(2) may reduce the effects of herbivory on the primary photochemistry controlling photosynthesis.     

The germination of mould spores at controlled humidities

Observations have been made on the influence of humidity on spore germination, the rate of elongation of the germ tubes and the production of asexual and sexual fructifications of various mould fungi. The humidity range at which the different species developed is given. Some of the Mucorales and certain pathogenic moulds required high humidities (100-93%) for their successful growth. Penicillium spp. had a wider humidity range (100-80%). Aspergillus spp. were able to grow under conditions of even more restricted moisture supply. Spores of members of the A. glaucus group, particularly, germinated and developed at humidities as low as 70-64%. The reasons for variations in the humidity range of the different species are discussed. The influence of the supply of nutrients on spore germination and subsequent mould growth is considered.     

The relative role of stomata in transpiration and assimilation

Summary The ways in which transpiration and assimilation depend on stomatal aperture are compared. It is shown that transpiration and assimilation are equally sensitive to change of stomatal aperture when the internal resistance to assimilation is equal to an effective resistance to evaporation which exists because of the coupling of heat and vapour exchanges between leaf and atmosphere. Generally the ratio of transpiration to assimilation changes with stomatal aperture in a manner which is determined by the relative magnitude of these resistances and on temperature. Some possible implications in relation to the optimal behaviour of stomata are discussed.Work done while J.H.T. held a New Zealand D.S.I.R. Fellowship.     

不同密度红桦幼苗苗冠结构与竞争对CO2浓度升高的响应

研究了两个种植密度下,红桦（Betula albosinensis）苗冠结构特征对CO2浓度的响应,在此基础上探讨了CO2浓度升高对植物竞争压力的影响。结果表明,冠幅、冠高、苗冠表面积和苗冠体积均受CO2浓度升高的影响而增加,但是受密度增加的影响而降低。CO2浓度升高对苗冠的促进效应在低密度条件下大于高密度处理,高密度条件下苗冠基本特征部分地受到CO2浓度升高的促进作用;升高种植密度的效应则在高CO2浓度条件下大于现行CO2浓度处理。高CO2浓度和高密度条件下,LDcpa（单位苗冠投影面积叶片数）、LDcv（单位苗冠体积叶片数）和苗冠底部枝条的枝角均低于相应的现行CO2浓度处理和低密度处理,这主要是由于冠幅和冠高的快速生长所造成的。升高CO2浓度对枝条长度的影响与枝条在主茎上所处位置有关。总之,升高CO2浓度有利于降低增加种植密度对苗冠所带来的负效应,而增加种植密度降低了升高CO2浓度的正效应。LDcpa和LDcv的降低表明,红桦在升高CO2浓度和种植密度的条件下,会作出积极的响应,从而缓解由于生长的增加所带来的竞争压力的增加。     

The production of toxins by Botrytis fabae in relation to growth of lesions on field bean leaves at different humidities

Filtrate extracts from liquid cultures of B. fabae and extracts from spreading chocolate spot lesions contained at least two heat-stable, light-labile phytotoxic compounds. Lesions similar in appearance to those of chocolate spot developed after injection of fractions containing these compounds into healthy bean leaves. Of 15 plant species injected with an extract from lesions, Vicia faba appeared to be the most susceptible to damage. Evidence is presented to support the hypothesis that under conditions of low humidity the concentrations of toxic compounds in an infected leaf become high enough to kill healthy cells surrounding infected tissue. The dead tissue then dries out preventing further fungal growth and lesion spread. In saturated air, however, the toxic compounds diffuse throughout the lamina and become too dilute to kill uninfected tissue. Tissue does not become desiccated and the fungus continues to spread.     

Influence of heavy-metal contamination on plant response to water availability in white birch,Betula papyrifera

Elevated concentrations of heavy metals in growth substrate are known to reduce root growth more than shoot growth. We hypothesized an increased sensitivity to drought in plants exposed to heavy metals. The hypothesis was tested using birch seedlings grown on a substrate with three levels of Cu–Ni containing slag (0%, 0.5% and 2.5%) mixed with sand, and were either well watered or exposed to drought. The experiment was conducted outdoors for 4 months. Both the slag addition and low substrate moisture reduced plant dry mass. There was a significant slag × moisture interaction. The effect of moisture was most pronounced on slag-free substrate, whereas at the highest slag addition level there was no growth response to moisture. Stem diameter, length of radial file and cell size showed similar responses, but error variation was high and the individual effects were not always significant. The general picture is, however, clear, the effect of moisture on all growth parameters increasing with decreasing slag concentration in the substrate. We conclude that metal-contaminated substrate leads to an inability of the plants to respond to improved soil moisture, an effect which can be seen even at metal levels which do not show any large growth reduction. In addition, reduced plant size, caused by heavy metals, results in feedbacks that increase the relative availability of water and mineral nutrients. At the highest slag addition level, substrate moisture was slightly higher than in controls, probably due to a reduced transpiration, and the senescence was slower, probably due to lower nutrient requirements of the smaller plants.